Hi, I'd like to let my forum users enter the amount they want to pay for a fixed time membership, having a minimum value defined by the admin.

Also, I don't want it to work as a paypal suscription (auto-renew), because it requires the user to have a credit card in their paypal account and also because you would have to deal with refunds or angry users who got charged because they forgot about the subscription.

So to summarize: 1) User-defined amount, 2) Work as "Buy Now" button instead of "Subscription", i.e. do NOT auto-renew.